Four Liebherr duty cycle crawler cranes, type HS 895 HD, HS 885 HD and two HS 855 HD with hydrofraise, are hard at work in Seattle on Contract U220.

Contract U220 is part of the University Link project, a 3.15-mile light rail extension between Downtown Seattle and the University of Washington. The project includes the construction of two 18-foot diameter, 11,400-foot long tunnels, the new University of Washington and the Capitol Hill stations. Furthermore the project includes the construction of the earth support for the University of Washington Station Box and the Cross-over structure. The tunnel work includes all civil works and cross-passages.

One HS 895 HD, one HS 885 HD and two HS 855 HD Liebherr crawler cranes were utilized at the site. The HS 885 HD crane was modified, and is a base carrier for the Evolution 3.5 hydrofraise, manufactured by Nicholson Construction's parent company, Soletanche Bachy. One of the HS 855 HD Liebherr crawler cranes also served as a base machine for a second Soletanche Bachy manufactured hydrofraise. The second Liebherr HS 855 HD, equipped with two 20-ton capacity winches, was utilized as a duty cycle crane, excavating the wall with a mechanical grab. The new Liebherr HS 895 HD crane was used as a service crane and set the reinforcement cages for the project.

The location of the project presents several challenges including restrictions on work based on the event schedule at the University, noise constraints due to residential areas to the south of the project and trucking restrictions due to traffic congestion. The Liebherr crane's low noise emission levels allowed operation of the equipment on extended shifts, the company said. Nicholson Construction saidthat the Liebherr cranes were selected for their "superior performance under duty cycle conditions and their reliability under difficult work conditions."

The Liebherr duty cycle crawler crane series is based, among other features, on a newly conceived superstructure with a robust and rigid box design. The maintenance-free Liebherr free-fall winches are installed as complete units and integrated drives and multi-disc brakes allow increased drum width with the same dimensions, increasing rope capacity on the first layer, for longer rope life. The main winches are driven via an axial piston displacement pump and a variable flow oil motor in closed circuit. This design allows precise work cycles for all winch movements. The supplied energy is ideally used in acceleration and braking of the winches and regained when operating in the power reducing mode, the company said.

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